Composite aluminum alloy engine cylinder



April 2, 1963 M. G. WHITFIELD EIAL 3,08

COMPOSITE ALUMINUM ALLOY ENGINE CYLINDER Filed June 23, 1958 INVENTORS.News/MAL GI MIT/FIELD fl EIYJELL CC'mn/Efi ATTORN EYS.

United States Patent 3,084,005 CUMPOSITE ALUMINUM ALLOY ENGINE CYLINDERMarshall G. Whitfield, Garden City, N.Y., and Wendell C. Cheney, LakeCity, Minn.; said Wendell C. Cheney assignor, by mesne assignments, toGould-National Batteries, Inc, St. Paul, Minn., a corporation ofDelaware Filed June 23, 1958, Ser. No. 743,659 Claims. (Cl. 309--2) Theinvention has to do with the provision of cylinders, particularly thosefor relatively small internal combustion engines. It has hitherto beenunderstood that by reason of the enhanced heat conductivity of lightmetals such as aluminum it would be advantageous to use such metals inconsiderable mass in connection with the cylinders. Thus, particularlyin air cooled engines, it has been found possible to provide a cylinderlining of cast iron, sheet steel or other forms of ferrous metal, and tocast aluminum around the outside of it in a mass which covers thecylinder lining and provides, for example, cooling fins.

It will be understood that such structures are not only relativelyexpensive, but involve the provision of a bond between the externalstructure of light metal and the ferrous cylinder lining. A bond isrequired not alone for mechanical reasons but to facilitate heattrans-fer from the ferrous lining to the external light metal body.Further, the presence of the ferrous lining interferes to some extentwith heat dissipation.

Attempts to manufacture engine cylinders from light metals alone havebeen made, but have given only a slight degree of satisfaction. Thecylinders do not wear well, even where their interior surfaces arechromium plated, or otherwise treated to make them more wear resistant.The light metals and their alloys are not well adapted to withstand thethermal and physical stresses of engine cylinder usage, and the numberof failures has been too high.

It is an object of the invention to provide an engine cylinder which isformed from light metals and light metal alloys but which does notpresent the disadvantages set forth above.

In one aspect, it is an object of the invention to provide a light metalengine cylinder in which the heat transfer is excellent, but which doesnot involve bonding difficulties.

These and other objects of the invention, which will be set forthhereinafter or will be apparent to the skilled worker in the art uponreading these specifications, are accomplished in that structure andprocedure of which certain exemplary embodiments will now be disclosed.Reference is made to the accompanying drawing which shows in section aportion of an exemplary engine cylinder indicating a preferred structureproduced in accordance with the present invention.

The term engine cylinder as used herein is employed in the broad sense.While a major utility of light metal cylinders lies in the field of aircooled engines where the cylinder embodies spaced cooling fins, it will'be understood that the invention is not limited thereto but may "ice beemployed in the construction of cylinders utilizing fluid cooling.Further, the term cylinder is not intended to be restricted to a caststructure embodying one cylinder alone, since the invention isapplicable to the manufacture of engine blocks containing a plurality ofcylinders. The specific embodiment chosen as illustrative is an aircooled engine cylinder, as will be apparent from the drawing, but thisis not limiting.

The invention contemplates a light metal engine cylinder, at least theinterior surface of which is made from a hypereutectic silicon-aluminumalloy as hereinafter defined.

As silicon is alloyed with aluminum up to about 13%, the silicon can bemade to combine with the aluminum, giving a hypoeutectic alloy ofsubstantially homogeneous character. As the amount of silicon increasesbeyond about 13% of the total weight of the alloy, the alloy takes on ahypereutectic character such that when the molten metal is cooled andfrozen some at least of the silicon precipitates in it. When the siliconcontent increases to about 17% or 18% or greater, the siliconprecipitates in massive particles easily discernible under themicroscope. These particles increase in size as the silicon contentincreases.

The silicon particles are very much harder than the alloy matrix inwhich they are bound; and it has been discovered that a light metalcylinder having an inner surface characterized by massive siliconprecipitation is very greatly superior in wear resistance to a cylindermade of light metal but with an interior surface not so characterized.If the quantity of silicon precipitation is sufficient, the 'cylinderwill show substantially no scoring even after long periods of use.

The greater the amount of precipitated silicon at the inner or workingsurface of the cylinder, the greater will be its wear resistance. It ispreferred in the practice of' the invention to employ at least at theinner or working surface of the cylinder an aluminum alloy containing atleast about 20% of silicon. As the silicon content increases the alloybecomes harder and also somewhat more difficult to machine and finish.The non-uniform character of the surface, i.e. the presence of massivesilicon particles in a matrix of softer alloy, results in a machined orfinished surface which is characterized by a sub-visual roughness orporosity which is useful in the retention of an oil film for lubricatingpurposes.

While a satisfactory hypereutectic alloy may be made from commerciallypure aluminum with the desired silicon addition, the presence of otheralloying ingredients is permissible, providing they are minor in amountand do not affect the essential action of the precipitated silicon.Alloying ingredients which may be employed along with silicon arecopper, nickel, magnesium, iron, titanium, manganese, zinc, cobalt andvanadium. Various alloys containing differing amounts of some or all ofthese substances may be produced, and will serve the purpose of theinvention.

Typical alloys which may be used in the practice of the invention areset forth in the following table:

Titanium.. Manganese...

Spec. Gr.--

Table I 21-23 20-22 19-21 23-25 17-19 17-19 21-22 0.9-1.2 1.4-1.81.3-1.7 0.8-1.3 4.7-5.3 1.0-1.2 1.01.2 2. 0-2. 4 1. 4-1. 6 05 0. 8-1. 33. 8-4. 2 1. 0-1. 2 1. 0-1. 2 -1. 25 0. 4-0. 8 1. 3-1 7 0. 8-1. 3 0.1-0. 6 1. 1-1. 3 0.5-0.6 70 max. 0. 7 0. 7 0.7 0. 3-0. 4 0. 4-0. 5 0.20.2 0.1 .05-0.1 .05-0.1 0. 6-0. 8 0 4-0. 6 0.2 0. 6-0. 8 0.7-0. 8 02 max0. 2 0. 2 0.2 0. 2 0.5-1.2 0.3-0.5 0.5-0.7 1.0-1.2

Typical physical characteristics for the first of the above alloys are:

Table II As another example, an alloy containing from 20% to 50%silicon, from 1% to 5% nickel, from .5% to 2.5% copper, from 1% to 3%magnesium, up to 1% vanadium and up to 1% antimony, the balance beingsubstantially all aluminum, may be used. Such an alloy is described inUnited States Patent 2,131,076 to Schwarz.

Complete cylinder structures may be cast from any or all of the alloysindicated above. It is characteristic of high silicon aluminum alloysthat they withstand thermal stresses better than pure aluminum; but atthe same time they are characterized by a brittleness which increaseswith the quantity of silicon. As a consequence, where engine cylindersare cast directly from high silicon aluminum alloys there is a limit tothe quantity of silicon which may be employed. Various expedients may beadopted to ameliorate this brittleness. It will be usual to subject thealloy castings to a de-growthing heat treatment, such as a treatment atabout 500 F. for a period of at least eight hours. Such a heat treatmentwill normally be effective in dropping the Brinnell hardness of analuminum alloy containing upwards of silicon from a value of about 150to a value of about 90. As will be evident from Table I above, such aheat treatment substantially increase the tensile strength of thecasting.

The cylinder castings may be made in sand molds or in permanent molds asdesired; but a chilling action on the metal at the inner surface of thecylinder may tend to cause the silicon to precipitate in smallerparticles.

There are certain materials which, when added in small amounts to thesilicon-aluminum alloy serve to break up the silicon masses therein,i.e. to cause the silicon to precipitate in smaller masses which have amore uniform distribution. Among such additives are phosphor copper(copper containing from about .1% to about 2.5 phosphorus) and zincphosphide. Other materials such as phosphorus pentachloride and sodiumand its salts have a similar effect; but are more ditficult to usebecause of the creation of fumes.

It will be understood further that the effect of brittleness can beameliorated to a useful degree by so design- 2:; the cylinder structurethat a sufficient mass of metal will be present at areas where excessivethermal and physical stresses are likely to be encountered.

Nevertheless, in the casting of solid cylinders of hypereutecticsilicon-aluminum alloy, even with control of the various factorsoutlined above, it is not generally feasible to use more than about ofsilicon.

Another aspect of the invention, however, presents no such limitation.In this aspect, a sleeve or cylinder lining is formed from ahypereutectic silicon-aluminum alloy, and a body of aluminum or aluminumalloy of different characteristics is cast thereagainst to form theremainder of the body of the cylinder and such fins, bosses and otherconfigurations as may be desired.

The exemplary structure, the formation of which has just been described,is illustrated in the figure where the numeral 1 indicates the preformedsleeve or cylinder of hypereutectic alloy, and the numeral 2 indicatesthe body or casting of aluminum or aluminum alloy of other character.

The sleeve structure formed from the hypereutectic alloy may contain asmuch silicon as desired and as is suitable for satisfactorymachineability irrespective of whether the alloy itself would be toobrittle to permit the casting of the entire cylinder structure of it.The reason for this is that when a body of aluminum or aluminum alloy ofdifferent characteristics is cast about the hypereutectic sleeve, thesleeve will be maintained in a condition of compression, while the lessbrittle chara eristics of the surrounding metal will satisfactorilyabsorb thermal and physical stresses.

The coefficient of expansion of aluminum is about .000023 per degreecentigrade. The coefficient of expansion of a hypereutecticsilicon-aluminum alloy containing upwards of about 20% silicon is verymuch less, being in the neighborhood of about .000016 per degreeCentigrade. Thus when aluminum is cast around the outside of asilicon-aluminum alloy and the structure is cooled, the aluminum will befound to be in tension and the hypereutectic sleeve in compression. Thissituation, although varying in degree, will persist throughout a widerange of temperature below the softening points of the metals. It willbe understood further that due to the dissipation of heat by the fins orjackets characteristic of the outer structure, the outer structure iskept below its softening point despite a high rate of heat transfer. Thesoftening point of the inner sleeve will be higher than that of theouter structure.

In the practice of the inventio it is not necessary that the differencebetween the metal of the inner sleeve and the metal cast about it be asgreat as that between a hypereutectic alloy containing at least about20% silicon on the one hand, and commercially pure aluminum on theother. The material of the outer casting may be and preferably is analuminum alloy containing a lesser quantity of silicon. Thus by way ofexample aluminum casting alloys known to the trade as A132 and D132which contain respectively 12% and 9% silicon, balance beingsubstantially all aluminum with normal impurities, may be used and willgenerally be found preferable to commercially pure aluminum in strengthand other characteristics. These are hypoeutectic alloys; buthypereutectic alloys containing above about 13% silicon may also beused. A considerable degree of ductility is desirable in the outer caststructure which will normally dictate a silicon content below about 18%;but it is only necessary to provide an outer structure which will haveductility to withstand the thermal and physical stresses to which thestructure may be put to use, and a difference of a few percent insilicon content will usually produce a composite structure characterizedby a useful degree of the tensional and compressional forces which havebeen described. But where an outer cast body is joined to ahypereutectic high silicon sleeve as herein described, the amount ofsilicon in the sleeve can be carried upwardly within wide limits and ingeneral to as much as 50% if desired.

In making the composite structure of this invention simple cylinders ofa hypereutectic aluminum alloy containing preferably more than 21%silicon are cast. The casting may be done in a baked sand mold, and ispreferably so accomplished, although permanent molds may be employed.The cylinder or sleeve so cast may then be cleaned in any suitable wayas by sand blasting, and may be located in a permanent or other mold tohave the body alloy cast against it. In a preferred procedure the highsilicon sleeve may be machined to an accurate wall thickness, say A; ofan inch, and may then be placed in a die casting machine and an aluminumdie casting alloy of lower silicon content may be caused to flow aboutthe present cast cylinder or sleeve and fill the mold to form a completeengine cylinder or block with cooling fins, bosses, flanges, reinforcingwebs, or other appropriate structural features.

The melting point of the metal of the sleeve structure will normally besufiiciently higher than that of the metal cast about it to preclude anymelting of the sleeve except at the surface of immediate contact.However, the sleeve may be located in the mold over a mandrel of metalat a lower temperature which will tend to cool the sleeve. No diflicultYis encountered with the formation of a bond since the molten metal tendsreadily to wet the sleeve. If the sleeve is insufiiciently cleaned or ischaracterized by oxide on its outer surface, the mold may be soconstructed and the pouring so accomplished as to produce a flow-byettect at the sleeve surface which will carry the oxide away. It has notbeen found necessary to employ interface coating metals such as tin,zinc or cadmium on the sleeve surface, although the invention would notbe avoided thereby.

The cylinder structures of this invention serve very well with lightmetal or heavy metal pistons having piston rings. They are also adaptedfor use with pistons not having rings, and in particular in thestructures claimed in the copending application of Cheney, Morehouse andWhitfield entitled, Cylinder and Piston Structures, Serial No. 777,036,filed November 28, 1958, now Patent No. 3,021,183.

In the cylinders of this invention the heat transfer through thecomposite section approaches that of a solid aluminum casting. Thehypereutectic sleeve which has been described may be de-growthed or heattreated prior to the casting of the body metal about it or a heattreatment may follow the construction of the entire unit, or both. Theuse of the separate sleeve as described permits the employment ofsilicon alloys in the sleeve or liner which are higher in siliconcontent than any commercial analysis available for ordinary castingwork, and higher than any alloys from which non-composite cylinderscould satisfactorily be produced.

Modifications may be made in the invention without departing from thespirit of it. The invention having been described in certain exemplaryembodiments, what is claimed as new and desired to be secured by LettersPatent is:

1. A light metal cylinder for an internal combustion engine, saidcylinder having a unitary body with an inner cylindrical surface forcoaction with a piston, said cylinder being made of metal consistingprincipally of aluminum, the metal at and adjacent said innercylindrical surface being a hypereutectic silicon-aluminum alloyscharacterized by precipitation of silicon in massive particles, saidalloy containing at least 17% silicon by weight, the remainder of thebody of said cylinder containing a lesser quantity of silicon.

2. A unitary light metal cylinder for an internal combustion engine,said cylinder having an inner cylindrical surface for coaction with apiston, the metal of said cylinder adjacent said surface being ahypereutectic siliconaluminum alloy containing substantially 20% to 50%silicon, the remainder of the metal of said cylinder consistingpreponderantly of aluminum and containing a lesser quantity of silicon.

3. A light metal cylinder for an internal combustion engine, saidcylinder consisting of an inner sleeve presenting an inner cylindricalsurface for coaction with a piston, and an outer body in metallic unionwith said sleeve, said sleeve being made of a silicon-aluminum alloycontaining substantially 20% to 50% silicon, and said body being made ofa metal consisting preponderantly of aluminum and conatining a lesseramount of silicon.

4. A light metal cylinder for an internal combustion engine, saidcylinder comprising an inner sleeve made of a hypereutecticsilicon-aluminum alloy, and an outer body in metallic union with saidsleeve and made of a hypoeutectic silicon-aluminum alloy.

5. A light metal cylinder for an internal combustion engine, saidcylinder comprising an inner sleeve and an outer body in metallic union,said sleeve being made of -a hypereuctic silicon-aluminum alloycharacterized by precipitation of silicon in massive particles, saidouter body being made of a metal consisting p-reponderantly of aluminumand having a coefiicient of expansion greater than that of the metal ofthe inner sleeve whereby the inner sleeve in said cylinder is maintainedin a state of compression.

6. The structure claimed in claim 5 wherein the metal of said innersleeve contains substantially 20% to 50% silicon.

7. The structure claimed in claim 5 wherein the metal of said innersleeve contains substantially 20% to 50% silicon, and wherein said outerbody contains less than about 13% silicon.

8. The structure claimed inrclaim 7 wherein the inner sleeve, at least,has the characteristic derived from a heat treatment at about 500 F. forat least about eight hours.

9. The structure claimed in claim 7 wherein the said inner sleevecontains a precipitation controlling agent chosen from a classconsisting of phosphor copper and zinc phosphide.

10. An article formed of light metal and having a body with an arcuatesurface which in use will have sliding contact with another element,said article being made of metal consisting principally of aluminum, themetal at and adjacent the said arcuate surface being a hypereutecticsilicon-aluminum alloy characterized by precipitation of silicon, saidalloy containing at least 17% silicon by weight, the remainder of thebody of said article containing a lesser quantity of silicon.

References Cited in the file of this patent UNITED STATES PATENTS1,799,837 Archer Apr. 7, 1931 1,822,877 Archer et al Sept. 15, 19311,886,396 Hainlen Nov. 8, 1932 1,940,922 Sterner-Rainer Dec. 26, 19332,024,767 Jetiries Dec. 17, 1935 2,106,590 Boegehold et a1. Ian. 25,1938 2,131,076 Schwarz Sept. 27, 1938 2,277,023 Steiner et a1. Mar. 17,1942 2,315,558 Somes Apr. 6, 1943 2,320,830 Ricardo et a1. June 1, 19432,462,139 Sparkes Feb. 22, 1949 2,656,593 Heintz Oct. 27, 1953 FOREIGNPATENTS 563,616 Great Britain Aug. 23, 1944

1. A LIGHT METAL CYLINDER FOR AN INTERNAL COMBUSTION ENGINE, SAIDCYLINDER HAVING A UNITY BODY WITH AN INNER CYLINDERICAL SURFACE FORCOACTION WITH A PISTON, SAID CYLINDER BEING MADE OF METAL CONSISTINGPRINCIPALLY OF ALUMINUM, THE METAL AT AND ADJACENT SAID INNER CYLIN-